The present invention relates generally to a method for transferring wafers in a semiconductor tape-peeling apparatus, and more particularly, to a wafer transfer method which prevents a wafer from being broken during a wafer transfer process.
In a semiconductor manufacturing process, a tape is generally adhered to the front-side (the surface where a wiring pattern is formed) of a wafer before carrying out back-side lapping in order to protect the wiring pattern of the wafer. Usually, the wafer is lapped to the thickness of, for example, 200 xcexcm by back-side lapping.
Referring to FIGS. 1 and 2, a conventional semiconductor tape-peeling apparatus includes a first cassette 1, a second cassette 2, a robot arm 3, a flat positioner 6, and a tape-peeling device 5. A suction means 7 is provided on the robot arm 3 to clamp and transfer a wafer 4 to be processed in the tape-peeling step.
Referring to FIGS. 2 and 3, the first cassette 1 includes twenty five wafer storage slots S01 to S25 (slots S06 to S25 are not shown). The wafers W01 to W25 (wafers W06 to W25 are not shown) are stored in the wafer storage slots S01 to S25 respectively of the first cassette 1. A tape (not shown) is adhered to the front-side of each of the wafers W01 to W25 that have been processed by back-side lapping. The thickness of each of the wafers W01 to W25 is about 200 xcexcm. It should be noted that the dimensions of these parts are not on the same scale, and the relationship among these parts is only shown schematically.
The operation method of the semiconductor tape-peeling apparatus are described hereinbelow. It should be noted that 25 wafers W01 to W25 are stored in the first cassette 1, but no wafer is stored in the second cassette 2 having the same construction as the first cassette 1. The second cassette 2 also includes 25 wafer storage slots S01 to S25 (not shown). Referring to FIGS. 2 and 3, the operation method includes the steps of:
(1) moving the robot arm 3 to the first cassette 1 so that the suction means 7 enters the first cassette 1;
(2) sucking the back-side of the wafer Wi(i=01 to 25) by the suction means 7 (it should be noted that the wafer Wi corresponds to the wafer 4 in FIG. 2 at this moment);
(3) activating the robot arm 3 to unload the wafer Wi from the first cassette 1;
(4) transferring the wafer Wi to the flat positioner 6;
(5) positioning the wafer Wi by the flat positioner 6 so that the flat side or notch of the wafer Wi directs to a predetermined direction;
(6) activating the robot arm 3 to suck the back-side of the wafer Wi by the suction means 7;
(7) transferring the wafer Wi to the tape-peeling device 5;
(8) peeling the tape on the wafer Wi by the tape-peeling device 5;
(9) activating the robot arm 3 to suck the back-side of the wafer Wi by the suction means 7;
(10) transferring the wafer Wi to the second cassette 2;
(11) storing the wafer Wi to the wafer storage slot Si(i=01 to 25) of the second cassette 2; and
(12) repeating steps (1) to (11) until the tapes on the wafers W01 to W25 are peeled and the wafers W01 to W25 are stored in the wafer storage slots S01 to S25 respectively.
Under the idealized condition, i.e., the condition in which the wafer 4 does not warp, each of the wafers W01 to W25 are stored in each of the wafer storage slots S01 to S25 as shown in FIG. 3. The positions of the suction means 7 where the suction means 7 sucks the wafers W01 to W25 are illustrated in FIG. 3.
Under the actual condition, when the tapes are adhered to the front-side of the wafers W01 to W25, the tapes are in a tensile mode. Therefore, the tapes adhered to the front-sides of the wafers W01 to W25 are capable of warping the center portions of the wafers W01 to W25 downwardly.
Furthermore, because each of the lapped wafers W01 to W25 is so thin that the strength thereof is not enough to resist the tensile force of the tape, and owing to the effect of the high temperature in the manufacturing process, each of the wafers W01 to W25 tends to warp easily, as shown in FIG. 4. As a result, when entering the first cassette 1, the wafers W01 to W25 can be crashed by the suction means 7.
In order to prevent the suction means 7 from crashing any of the wafers W01 to W25, a method for repositioning the suction means 7 is adopted, as shown in FIG. 5. According to this method, the position of the suction means 7 is adjusted to avoid crashing the wafers W01 to W25. However, because the warpage degrees of the wafers W01 to W25 are not uniform, the wafers W01 to W25 can still be crashed by the suction means 7, as shown in FIG. 6.
Referring to FIG. 7, vacuuming conduits 71 are formed on two sides of the suction means 7. The wafer W01 is sucked downwardly by the vacuuming conduits 71. The deformation of the wafer W01 becomes large, and the wafer W01 can be damaged.
Thus, the above problem cannot be completely solved using the method for repositioning the suction means 7. Furthermore, an unexpected damage can be caused when using the method for sucking the back-side of the wafer.
It is therefore an object of the present invention to provide a wafer transfer method for use with a semiconductor tape-peeling apparatus so as to prevent the robot arm from crashing the wafer.
In accordance with the first aspect of the invention, a method for transferring wafers in a semiconductor tape-peeling apparatus is provided. The semiconductor tape-peeling apparatus comprises: a first cassette for storing a plurality of wafers, each of the wafers having a front-side to which a tape is adhered and a back-side; and a robot arm including a suction means for sucking and transferring the wafers, the wafer transfer method comprises the step of:
sucking the front side of the uppermost one of the wafers stored in the first cassette and unloading the wafer.
According to the above wafer transfer method, the undesired result that the warped wafers stored in the cassette are crashed by the robot arm can be avoided.
The semiconductor tape-peeling apparatus further comprises a flat positioner, a tape-peeling device, and a second cassette, the wafer transfer method further comprises the steps of: transferring the wafer to the flat positioner; positioning the wafer by the flat positioner; sucking the back-side of the wafer by the robot arm; transferring the wafer to the tape-peeling device; peeling the tape on the wafer by the tape-peeling device; sucking the back-side of the wafer; and transferring the wafer to the second cassette.